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Cenis, Mont(môN sənē`), Ital. Moncenisio, Alpine pass, 6,831 ft (2,082 m) high, on the French-Italian border. It is one of the great invasion routes in Italian history. Napoleon I built a new road there in 1810. In 1871, the Mont Cenis railroad tunnel (Frejus Tunnel) was built approximately 30 mi (48 km) away, connecting the towns of Mondane, France and Bardonecchia, Italy. As the first rock tunnel of its sort, it pioneered many techniques and represents a landmark in engineering. It is still one of the world's largest (8 mi/13 km) railroad tunnels.
(in Italian, Monte Cenisio), a pass between the Cottian and Graian Alps in France, close to the Italian border. Elevation, 2,083 m. The pass connects the Isère and Dora Riparia river basins and is traversed by the Grenoble-Turin highway. To the southwest, beneath the Fréjus pass, is the Mont Cenis railroad tunnel.